 Programs were mostly written in machine code.Bugs that previously went unnoticed became prominent when 1ESS was brought to big cities with heavy telephone traffic, and delayed the full adoption of the system for a few years.Temporary fixes included the Service Link Network (SLN), which did approximately the job of the Incoming Register Link and Ringing Selection Switch of the 5XB switch, thus diminishing CPU load and decreasing response times for incoming calls, and a Signal Processor (SP) or peripheral computer of only one bay, to handle simple but time consuming tasks such as the timing and counting of Dial Pulses.