Microprocessor The T6400 model uses an 80486SX-25 microprocessor that operates at 25 MHz. The T6400DX model uses an 80486DX-33 microprocessor that operates at 33 MHz. Math co-processor The T6400DX model has a Numeric Data Processor (NDP) inside the CPU. The T6400 comes with a built-in socket for an 80486DX-33 which incorporates a Numeric Data Processing Unit (NDP). Cache memory The T6400 has an 8 KB cache memory which is stored in the microprocessor. Disk storage The T6400 has an internal 120 or 200 Megabyte (MB) Hard Disk Drive (HDD) with an average access time of 19 milliseconds. A 3.5-inch Floppy Disk Drive (FDD) supports 2HD floppy disks (1.44 Mbytes) and 2DD floppy disks (720 Kbytes).