The Wikipedia articles are a reasonable place to start for a quick overview:
http://en.wikipedia.org/wiki/Intel_8080
http://en.wikipedia.org/wiki/Intel_8085:
The Intel 8085 is an 8-bit microprocessor introduced by Intel in 1977. It was binary compatible with the more-famous Intel 8080 but required less supporting hardware, thus allowing simpler and less expensive microcomputer systems to be built.
The "5" in the model number came from the fact that the 8085 requires only a +5-volt (V) power supply rather than the +5V, −5V and +12V supplies the 8080 needed. Both processors were sometimes used in computers running the CP/M operating system, and the 8085 also saw use as a microcontroller, by virtue of its low component count. Both designs were eclipsed for desktop computers by the compatible Zilog Z80, which took over most of the CP/M computer market as well as taking a share of the booming home computer market in the early-to-mid-1980s.
The 8085 is a conventional von Neumann design based on the Intel 8080. Unlike the 8080 it does not multiplex state signals onto the data bus, but the 8-bit data bus was instead multiplexed with the lower part of the 16-bit address bus to limit the number of pins to 40. Pin No. 40 is used for the power supply (+5v) and pin No. 20 for ground. Pin No. 39 is used as the hold pin. Pins No. 15 to No. 8 are generally used for address buses. The processor was designed using nMOS circuitry and the later "H" versions were implemented in Intel's enhanced nMOS process called HMOS, originally developed for fast static RAM products. Only a 5 Volt supply is needed, like competing processors and unlike the 8080. The 8085 uses approximately 6,500 transistors.[1]
The 8085 incorporates the functions of the 8224 (clock generator) and the 8228 (system controller), increasing the level of integration. A downside compared to similar contemporary designs (such as the Z80) was the fact that the buses required demultiplexing; however, address latches in the Intel 8155, 8355, and 8755 memory chips allowed a direct interface, so an 8085 along with these chips was almost a complete system.
http://en.wikipedia.org/wiki/Zilog_Z80
The Z80 offered many real improvements over the 8080:
An enhanced instruction set including bit manipulation, block move, block I/O, and byte search instructions
New IX and IY index registers with instructions for direct base+offset addressing
A better interrupt system
A more automatic and general vectorized interrupt system, mode 2, as well as a fixed vector interrupt system, mode 1, for simple systems with minimal hardware (mode 0 being the 8080-compatible mode).
A non maskable interrupt (NMI) which can be used to respond to power down situations and/or other high priority events (and allowing a minimalistic Z80 system to easily implement a two-level interrupt scheme in mode 1).
Two separate register files, which could be quickly switched, to speed up response to interrupts
Less hardware required for power supply, clock generation and interface to memory and I/O
Single 5 volt power supply (the 8080 needed -5V/+5V/+12V)
Single-phase 5 V clock (the 8080 needed a two-phase high-amplitude clock generator)
A built-in DRAM refresh mechanism that would otherwise have to be provided by external circuitry
Non-multiplexed buses (the 8080 had state-signals multiplexed onto the data bus)
The Z80 took over from the 8080 and its offspring, the 8085, in the processor market, and became one of the most popular 8-bit CPUs. Perhaps a key to the initial success of the Z80 was the built-in DRAM refresh, and other features which allowed systems to be built with fewer support chips (later on, most Z80 systems have been embedded systems, which typically uses static RAM and hence does not need this refresh).
