Computing History · Cluster
Microprocessor Revolution
Personal computing and its software.
- 01 Multiplexed Address and Data Buses in a Forty-Pin Package Multiplexed address and data pins let a processor with more address lines than pins reach memory, at the cost of an external latch and a shortened access window.
- 02 Two Address Spaces: Port-Mapped and Memory-Mapped I/O Decoding Why the 8080 family reserved a separate 256-byte I/O space, how the control signals distinguish it from memory, and what each arrangement costs in address decoding and instruction width.
- 03 Zero Page Addressing and the Economics of Eight-Bit Instructions Placing the first 256 bytes of memory at the centre of the instruction set traded address range for instruction length, and shaped how eight-bit code was written.
- 04 Framebuffer Arithmetic: What a Bitmap Mode Costs in Memory Character cells versus linear bitmaps, the byte counts each requires at common resolutions, and why early machines split the difference with attribute bytes and planar layouts.
- 05 Cycle Counting When the Video Circuit Steals the Bus How display refresh suspends the processor on shared-memory machines, why the stolen cycles are unevenly distributed, and how timing loops are written so the loss is measurable.
- 06 MFM Encoding and the Fixed Geometry of a Floppy Sector Why magnetic media store clock bits alongside data, how a sector is framed by address marks and gaps, and how FAT12 packs a cluster chain into twelve-bit entries.
- 07 Interrupt Vectors as the First Hardware Abstraction Layer The real-mode vector table turned firmware entry points into a stable calling convention, letting programs reach disks, video, and keyboards without knowing which adapter was installed.
- 08 Segment Arithmetic and the One-Megabyte Wall How sixteen-bit segment registers produce a twenty-bit address, why the resulting space wraps at the top, and what the A20 gate and the high memory area cost.
- 09 Resident Programs and the Reentrancy Problem in DOS Terminate-and-stay-resident code hooks the timer or keyboard interrupt, but DOS itself is not reentrant, so a resident handler must either defer work or re-enter through a documented flag.
- 10 DOS Extenders and the Cost of Leaving Real Mode Loading a protected-mode segment table, moving the interrupt path into extended memory, and reflecting calls back to real mode: what a 32-bit program had to build before it could run.