Intel 4040

Intel 4040

A white ceramic C4040 variant
General information
Launched	1974
Discontinued	1981[1]
Common manufacturer	Intel
Performance
Max. CPU clock rate	500 kHz to 740 kHz
Data width	4 bits
Address width	12 bits (multiplexed)
Architecture and classification
Technology node	10 μm process
Instruction set	4-bit (BCD-oriented)
Physical specifications
Transistors	3,000[2]
Package	24-pin DIP
History
Predecessor	Intel 4004
Support status
Unsupported

The Intel 4040 ("forty-forty") is the second 4-bit microprocessor designed and manufactured by Intel. Introduced in 1974 as a successor to the Intel 4004, the 4040 was produced with a 10 μm process and includes silicon gate enhancement-load PMOS logic technology. The 4040 contained 3,000 transistors^[2] and could execute approximately 62,000 instructions per second.

General performance, bus layout and arithmetic logic unit (ALU) were identical to the 4004. The main improvement was to use a larger 24-pin dual inline package, giving it 8 more pins than the 16-pin 4004. Two of these were used to implement interrupts, which were lacking in the 4004 and considered a major oversight. Two more implemented a halt/stop system, which put the processor into a low-power mode and also allowed for single-step operation that made debugging much easier. Another pin was used to bank select a second read only memory (ROM), doubling the amount of ROM the processor could address compared to the 4004.

To make use of these new pins, the instruction set was expanded, increasing it to 60 instructions from the original 46. Additionally, the internal register file and pushdown stack were expanded to support rapid interrupt processing.