Re-read: how many total bytes does the ENIAC register memory occupy — pure count from specs: - Portal da Acústica

Understanding the Context

Understanding ENIAC’s Memory Structure

ENIAC, completed in 1945 at the University of Pennsylvania, was revolutionary not just for its programmability but also for its high-speed electronic computation. Unlike modern stored-program computers, ENIAC relied on registers — fast, on-board memory locations directly accessible by its 20 vacuum tubes-based functional units — to store intermediate values and program operands.

But ENIAC’s architecture differed fundamentally from today’s systems:

• It featured no traditional registers as small, dedicated storage units like modern CPUs have.
  
• Instead, data was loaded into workspace cells on its 10 accumulators and sequential memory blocks, but register-like functions were embedded in its computation modules rather than as persistent byte storage.

Key Insights

What About Its “Register” Memory?

ENIAC’s “register registers” were limited and not persistent in the modern sense. The machine’s accumulator (a 10-bit register per functional unit) could hold a single 10-bit value — equivalent to 1.25 bytes, but this register was programmatic, updateable, and not organized like a fixed-size register file.

Official documentation and engineering reports from the Moore School (ENIAC’s birthplace) specify:

• ENIAC’s 10 accumulators could each hold a value of 10 decimal digits (not binary), totaling 10 × 10 = 100 digits — but this is decimal, not binary storage.
  
• The machine used a 16-word arcade memory (core memory-like transgenic storage), but this was external and separate from the registers.
  
• Crucially, no dedicated register memory in the modern sense occupied a fixed byte count. ENIAC’s registers were dynamic, reused, and tied directly to its rapidly swapping vacuum tube logic.

Pure Byte Count from Specs

Final Thoughts

If we strictly count only the fixed, dedicated storage spaces in ENIAC’s register-like units as defined in its 1946 technical report, the total pure byte count of register-equivalent storage is zero — because ENIAC lacked static, symmetric registers storing bytes persistently.

However, based on maximum simultaneous active register-like storage during computation, a conservative estimate during peak operation shows minimal but realooking integration:

• ENIAC had 10 accumulators, each holding a 10-bit value → ~1.25 bytes usable at once.
  
• In a busy computation, up to 5–6 of these accumulators might be actively storing operands in parallel at any time.

Thus, at peak operation, ENIAC’s register-equivalent working memory occupied roughly 7.5–10 bits (0.938–1.25 bytes) at once — a flickering, high-speed subset, not a stable countable register.

Conclusion

In pure count from ENIAC’s official specs: