The KS-2020 used RM03 or RP06 disk drives. Up to 8 disks, in any combination, on a single MASSBUS.

The KL-10 used RP06 or RP20 disk drives. Up to 8 disks per MASSBUS. (Each RP20 spindle counts as 2 disks.)


(From the 1981 edition of the "DECsystem-10 Technical Summary".)

The disk subsystems provide high performance and reliability. Disk features include accurate server positioning, error correction, and offset positioning recovery. Table 7-1 summarizes the capactities and speeds of the disk devices.

To support the performance and reliability features of the system's disk devices, the operating system's disk device drivers provide comprehensive error recovery algorithms (for example, ECC and offset recovery for disk) and log all device errors.

Disk controllers allow several drives to preforma simultaneous seek operations. Since the controller is not busy during seek operations, data transfers on one drive can overlap seeks in progress on other drives. If more than one drive is on the same controller, overlapped seeks will accelerate processing for the disks on that controller. Overlapped seeks increase throughput by decreasing the effective access time.

Table 7-1
Disk Devices
Disk Type Capacity Peak Transfer
Rate (Kbytes
per second)
Average Seek
Time (ms)
Average Rotational
Latency (ms)
Interface Maximum
Drives per
RM03 Removable 67 Mb 1200 30 8.30 MASBUSS 8
RP06 Removable 176 Mb 806 28 8.33 MASBUSS 8
RP20 Non-removable 967 Mb 1200 25 8.33 MASBUSS 4 *
* Two spindles per drive.     K = 1,024; M = 1,000,000

RM03 Disk Pack Subsystem (KS system only)

RM03 The RM03 is a top-loading, free-standing disk drive housed in a dedicated cabinet. Subsystems are expandable to eight disk drives or 536 Mb. The RM03 has a formatted capacity of 67 megabytes and an average access time of 38 milliseconds. Its maximum transfer rate is 250,000 36-bit words per second. The RM03 does 18-bit NPR data transfers over a UNIBUS and 36-bit NPR data transfers over the KS10 backplane bus.
Stand-alone RM03 disk.

RP06 Disk Pack Subsystem (KS and KL systems)

RP06 The RP06 is a large capacity disk drive. [176,000,000 bytes; the equivalent of the IBM 3330-II disk drive.] This disk offers both high performance and a low price per megabyte of storage. It uses a removable disk pack and has a wide variety of large disk features.

RM03 and RP06 disk drives can be mised on the same RH11 controller on a KS10; however they can not be mised within the same logical file structure.

Two RP06 units in front of a KL-2060.

RTP20 Disk Subsystem (KL systems only)

RP20 The RTP20 is the highest capacity disk offered by DIGITAL. The RTP20 consists of an RP20 disk drive and controller. THe RP20 is a dual-spindle device with a formatted capacity of 967 megabytes. Master Subystems are packages to include an RH20/DX20 Channel, RTP20 Controller, and RP20 Master Disk. When additional capacity is required, the subsystem can be expanded to include up to three add-on drives (1200 megabytes unformatted).

Each RP20 data module has fifteen recording surfaces with two read/write heads per surface and a transfer rate of 1.2 megabytes per second with a 25 ms averate access time. Each data module may transfer independently with the dual-port feature.

DX20 (MASSBUS to IBM bus&tag conversion), RTP20 string controller, two RP20 disk units (two spindles each).

Maintained by Joe Smith at