The Rise and Fall of SPARC: Why No One Misses It

The Rise and Fall of SPARC

Once upon a time, there was a company called Sun Microsystems, founded by legendary computer engineers like Bill Joy. Sun shipped products across a remarkable range of domains: programming languages (Java), databases (MySQL, though it originated at a Swedish company), operating systems (SunOS and Solaris), file systems (ZFS), and their own processor architecture (SPARC). Their workstations and servers were enormously popular throughout the 1990s, when enterprises ran Java applications on SPARC machines powered by Solaris. But like many technology companies of that era, Sun suffered massive losses after the dot-com bubble burst. To make matters worse, the industry was migrating toward Intel x86, while Sun continued to bet on SPARC. The result was Oracle's acquisition of Sun Microsystems in 2010.

What became of Sun's product portfolio after the acquisition? Key Java developers left the team. Oracle favored its own database over MySQL, and PostgreSQL stepped in to fill the vacuum in both community and enterprise adoption. Solaris is now effectively dead — its engineering team was laid off, Oracle halted development after Solaris 11, and shifted its focus to Oracle Linux. Oracle also abandoned ZFS development; its open-source fork, OpenZFS, now leads ZFS development. Oracle could have re-licensed ZFS as GPLv2 for Linux, as SGI did with XFS, but the company chose to invest in Btrfs instead.

You can probably guess what happened to SPARC. Oracle gave it up. No new processor has shipped from Oracle since the SPARC M8 in 2017, and although companies like Fujitsu continued working on SPARC for a time, they too eventually abandoned it in favor of Arm. Were developers sad to see SPARC go? Not in the slightest — and in this post, I'll explain why.

The Ugly Aspects of SPARC

Licensing

Sun Microsystems open-sourced two SPARC implementations — UltraSPARC T1 and T2 — under the OpenSPARC project. Like OpenSolaris, the project was shut down after Oracle's acquisition. Both designs are dated and slow. While T2 offers 8 cores and 64 threads, its maximum clock rate is just 1.6 GHz. Compare that to the contemporary IBM POWER6, which delivered 2 cores at 5.0 GHz. T2's closed-source successor, the T3, provides 16 cores at 1.67 GHz, while POWER7 offers 8 cores at 4.25 GHz — both launched in 2010. Despite SPARC neither dominating the market nor offering best-in-class performance, the open-source implementations were released under GPLv2, which effectively deterred companies from building commercial SPARC processors.

There are precedents for commercial products open-sourced under GPLv2 — early id Tech engines, for instance. But id Software chose GPL specifically to encourage modding, and the strategy served that goal well. SPARC, by contrast, gained nothing from the GPLv2 license. This is a key reason we never saw new SPARC processors from third parties.

What about designing a SPARC chip from the ground up? The SPARC ISA is fully open, non-proprietary, and royalty-free, but you still need a license from SPARC International, the organization governing the architecture:

SPARC specifications are available for licensing by any individual or entity, giving licensees flexibility and freedom to design their own solution. To obtain a license, please contact us at info@sparc.org Control of the SPARC architecture is administered and licensed by SPARC International, Inc. (“SI”). Membership is open to everyone. Click here to apply for membership.

...and the membership application page returns a 404 Not Found.

By contrast, OpenPOWER has required no licensing from IBM since it was transferred to the Linux Foundation in 2019, making it far more accessible for hobbyists and third parties to create their own designs.

Big-Endian Legacy

SPARC V9 is bi-endian in name only. Its roots are firmly planted in big-endian territory: it only supports big-endian instructions, and its bi-endian capability is limited to load/store operations or accessing data from little-endian devices through MMU configuration. As a result, operating systems targeting SPARC are inherently big-endian — a stance increasingly at odds with modern computing trends.

Register Windows

Now for the technical aspects of SPARC.

Programmers and compilers see 32 registers, similar to Arm and MIPS, but the hardware actually contains 128 internal registers. The visible 32 are divided into four groups:

• Global (%g0–%g7): Always visible across all contexts.
• In (%i0–%i7): Arguments passed from the caller.
• Local (%l0–%l7): Scratch space for the current function.
• Out (%o0–%o7): Arguments to be passed to the callee.

The rotation mechanism works via the save instruction at function entry. The previous function's Out registers seamlessly become the new function's In registers. This makes function calls remarkably fast, since you rarely need to spill registers to the stack.

However, if you nest too many function calls, you exhaust the physical hardware windows. The CPU then triggers a window overflow trap, forcing the OS to manually save registers to memory. This adds significant complexity to context switching and exception handling, making it a persistent pain point for systems programmers.

Branch Delay Slots

In early RISC pipelines, by the time the CPU recognized that a branch was being taken, it had already begun fetching the next sequential instruction. Rather than discarding that work and stalling the pipeline, SPARC's designers decided that the instruction immediately following a branch would always execute, regardless of whether the branch is taken.

For example:

cmp   %l0, %l1      ! Compare two values
be    label         ! Branch if equal
add   %g1, 1, %g1   ! <--- DELAY SLOT: Executes BEFORE the jump happens

This meant compilers had to be clever enough to find a useful instruction to fill that slot. When they couldn't, they were forced to insert a nop, wasting both space and cycles. Modern processors rely on branch prediction, rendering delay slots an obsolete burden for both compilers and assembly programmers.

Annul Bit

To mitigate the awkwardness of delay slots, SPARC's designers introduced another layer of complexity: the annul bit. This modifier on branch instructions causes the delay slot instruction to be skipped (annulled) if the branch is not taken. A patch on a patch — added complexity to address the consequences of an earlier design choice.

Condition Codes

Unlike some modern architectures that allow comparison results to be stored in general-purpose registers, SPARC uses a centralized Integer Condition Code (icc) register. Instructions like addcc or subcc (where the cc suffix denotes condition code updates) set four flags:

• N: Negative
• Z: Zero
• V: Overflow
• C: Carry

This creates a data dependency bottleneck. If two independent additions are in flight simultaneously, they both contend for the same icc register. This makes out-of-order execution — the cornerstone of modern high-performance CPUs — significantly harder to implement, since the processor must carefully track ownership of the status flags at every stage.

Synthetic Instructions

SPARC assembly is full of pseudo-instructions. For example, there is no hardware clr (clear) instruction. To clear a register, you write or %g0, %g0, %dst. These synthetic instructions are assembler conveniences that paper over gaps in the actual ISA.

Putting It All Together

Here's a concrete example that illustrates these quirks in action — a simple sum_array function in SPARC assembly:

! Standard SPARC calling convention
! %i0: base address of array
! %i1: number of elements (n)
! %i0: return value (at the end)

sum_array:
    save    %sp, -96, %sp       ! ROTATE WINDOW: Allocate new stack frame
                                ! %i0 and %i1 are now the input arguments

    clr     %l0                 ! %l0 = sum (Synthetic: actually 'or %g0, 0, %l0')
    clr     %l1                 ! %l1 = index i

loop:
    cmp     %l1, %i1            ! Compare i with n (updates icc)
    bge     done                ! Branch if i >= n
    nop                         ! DELAY SLOT: No safe instruction to place here

    sll     %l1, 2, %l2         ! %l2 = i * 4 (shift left by 2 for word offset)
    ld      [%i0 + %l2], %l3    ! Load array[i] into %l3

    add     %l0, %l3, %l0       ! sum = sum + array[i]

    ba      loop                ! Branch always back to loop start
    inc     %l1                 ! DELAY SLOT: Increment executes AFTER the jump

done:
    mov     %l0, %i0            ! Place sum in return register
    ret                         ! Return to caller
    restore                     ! DELAY SLOT: Restores the previous register window

Several SPARC idioms are on full display here:

The save and restore dance. The save instruction at entry shifts the register window — the caller's %o0 (the array pointer) becomes this function's %i0. The restore at the end shifts it back, and it executes in the delay slot of ret, so the CPU returns and restores the register window simultaneously.

The wasted nop. After bge done, the compiler couldn't safely place the sll instruction in the delay slot, because if the branch were taken, computing the offset would be incorrect. The result: a wasted cycle.

The useful delay slot. At the loop's end, inc %l1 is placed after ba loop. The CPU initiates the jump but completes the increment on its way out — a classic SPARC scheduling optimization.

Synthetic clr. clr %l0 is simply an assembler alias for or %g0, %g0, %l0. Since %g0 is hardwired to zero, OR-ing zero with zero reliably clears the destination register.

Conclusion

Even if SPARC had adopted a truly open licensing model like OpenPOWER, I suspect adoption would have remained minimal due to these accumulated architectural quirks. As of 2026, RISC-V is leading the open ISA movement, and many engineers — myself included — consider its design superior to its predecessors. This is no accident: RISC-V was explicitly designed to address the pain points of earlier architectures like SPARC, MIPS, and others.

Still, as the flagship processor architecture of Sun Microsystems, SPARC offers a fascinating window into how microarchitects of a previous generation envisioned the future of computing — and a valuable reminder that even clever engineering decisions can become liabilities as the landscape evolves.